We report a case study of a patient suffering from T-lymphoblastic lymphoma, for whom autologous T-cell-depleted bone marrow transplantation was carried out. Low-dose cyclosporin A (CsA) was administered just after autologous bone marrow transplantation (ABMT) for induction of autologous graft-versus-host disease. Three months later, the lymphoma relapsed with marked monoclonal gammopathy of the immunoglobulin A type, which had not been seen before ABMT. It is suggested that the regrowth of the lymphoma cells was related to the maturation of B cells or the secretion of immunoglobulins from plasma cells, associated with some cytokines produced under the condition of an abnormal immunological circumstance after ABMT plus CsA.